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Full text of "Text Book Of Mechanical Engineering"

348

Riveting the Boiler.

if

' I' '

upon them. The inner laps at the joints b b b must of course be
tapered, but no holes are yet drilled there, or through any of the
tapered pieces.

Fix all plates of both chambers, including Fox tubes, with
temporary bolts; and, laying each upon its back, drill with
Horizontal Drill all the rivet holes, as spaced on the cover plates.
Mark out and drill to tapping size the stay holes in the mid cover
plate of one chamber only, and drill also the holes for the girder-
stay bolts. Set up both chambers in position as at 29 by bolting
through the rivet holes, and blocking below. Obtain level position
with great exactness, then draw horizontal tube centres by
squaring from the roof, and the vertical lines from the middle
plates. They are afterwards drilled to correspond with II. The
mid stay holes are marked from one chamber to the other by a
punch 30, of the same diameter as the tapping size of the holes,
and afterwards drilled by Horizontal Drill.

The Girder or Roof Stays are now cut out by band saw, being
clamped together, and are next fitted to the roof, as shewn in

Fig. 311-

The Band Saw is a very useful tool, but requires some
attention to keep it keen. The tool at 31 is a roughened steel
helix, rotated by gearing to sharpen the saw teeth as the band is
advanced.

Riveting the Boiler.—The Front and Back Plates may
now be put together in a Fixed Riveter as *at^3 2, and the ring
plates attached by the same machine up to the condition L,
Plate XVI. But the Back Plate,must either be put in by hand
or semi-hand process, or by the machine at p, Plate XVI. The
combustion chamber (after riveting up) is first inserted, and laid
loosely within the shell. Then, if hand-riveting be used, the rivet
will appear like that at 38, the flat finish being obtained by very
quick consecutive blows from riveting hammers used by two work-
men, while a third ' holds up' a cupping tool within the boiler.
The hammering is continued on both sides after the rivet is cold,
as a sort of caulking. A pneumatic hammer is employed in
some works, as at 33, where a lever vibrates from a crank plate
driven by a belt, while the hammer end is provided with a
pneumatic dashpot or cushion, giving a finish like 36. The